This invention relates to improvements in a reduction projection aligner system for use in semiconductor production.
The reduction projection aligner system is typically used for semiconductor production and forms the patterns of semiconductor integrated circuits, such as ICs and LSIs, directly on wafers. In many conventional reduction projection aligner systems, the wafer and a reticle (a glass plate on which an original pattern is depicted) are positioned independently of each other. More specifically, the reticle is positioned by visually detecting two typical portions on the reticle with a reticle positioning optical microscope and is fixed onto the body of the apparatus, while the wafer is positioned by visually detecting two typical portions on the wafer with a wafer positioning optical microscope and is fixed onto the same body. With the method in which the whole wafer is positioned on the basis of the two typical portions on the wafer in this manner, the precision of the alignment between the reticle and the wafer depends principally on the positioning precision of the wafer, which forms a serious hindrance to the enhancement of the alignment precision. In addition, it is impossible to align the reticle and the wafer if an error in the arrangement of the pattern on the wafer attributed to the anisotropic expansion or contraction of the wafer occurs during the manufacturing of the wafer.
Therefore, in order to eliminate such disadvantages and to make high precision alignment of both the reticle and the wafer possible, there has been devised a method as shown in FIG. 1 wherein the position of a wafer is relatively detected through a reticle as well as a reduction lens (refer to Japanese patent application Laid Open No. 54-93974).
In the reduction projection aligner system shown in FIG. 1, a pattern to be used for positioning is formed on the wafer 4 by a preceding step and this pattern is illuminated by a light guide 7 through a reference pattern 5 formed on an edge of the reticle 2 and further through a reduction lens 3. Using the reflected light from the wafer 4, the positioning pattern on the wafer 4 is focused on the reticle 2. On the other hand, in order to detect the position of the reticle 2, the reference pattern 5 on the reticle 2 is illuminated by a light guide 6. Thus, the reflected lights from the wafer 4 and the reticle 2 are projected onto the position occupied by a slit 10 by means of a magnifying optical system 9, the distance of movement of the slit 10 is measured by a uniaxial movable table 12 and a measuring machine 13, and the output from a photo-detector 11 corresponding to the position of the slit 10 is detected, whereby the relative positions of the reticle 2 and the wafer 4 are detected.
With this system, however, the predetermined reference pattern 5 needs to be formed in a specified position on the reticle 2 separately from a circuit pattern carried by the reticle and a reticle positioning pattern which is used for positioning the reticle 2 with respect to a holder 14. This provision of the reference pattern 5 forms a serious hindrance in preparing the reticle. Moreover, any arrangement error of the reference pattern 5 with respect to the circuit pattern on the reticle results in an alignment error between the reticle 2 and the wafer 4. Further, since the relative positions of the reticle 2 and the wafer 4 are detected, an optical system for illuminating the reticle surface which consists of the light guide 6 and a mirror 8 must be installed; however, such installation is very difficult in practice. In the figure, numeral 1 designates a condensing lens in the primary optical path of the system.